PROJECT SUMMARY/ABSTRACT The URI-led STEEP (Sources, Transport, Exposure and Effects of PFASs) proposes to aid the Superfund Research Program in addressing the emerging and expanding problem of poly- and perfluorinated alkyl substances (PFASs) contamination. PFASs are industrial compounds that have been manufactured since the 1950s for use in a myriad of products due to their unique oil and water repellent properties. The environmental dissemination and the human health effects of PFASs are only beginning to emerge. Thus, the U.S. EPA limits for PFAS contamination of drinking water remain provisional since they were first published in 2009. In the recently released 2015 draft ToxProfile, ATSDR highlighted uncertainties and disregarded recent reports on adverse human health effects of PFAS exposures from epidemiological studies. Thus, the need for improved risk characterization is urgent and timely. STEEP aims to better understand the pathways of PFAS contamination from entry into the environment through groundwater contamination, dispersal through the food web, and distribution to vulnerable human populations during early development, in part through breast milk. Specifically, STEEP will characterize sources of PFAS through in situ groundwater measurements combined with geochemical modeling to assess transport and fate (Project 1). The biomedical studies will assess the relationship of PFAS to risk of immune dysfunction and metabolic abnormalities, to be used to derive benchmark doses levels for PFASs for improved risk characterization. Due to the hypersusceptibility during early development, the research will focus on the impact of in utero and early postnatal PFAS exposures on sensitive indicators of organ dysfunctions through parallel human epidemiologic studies (Project 2) and rodent model studies (Project 3). Then, environmental engineering and chemistry research will support the development and deployment of in situ passive sampling techniques for PFAS and their precursors in water (Project 4). STEEP will thereby address limitations in the current understanding of human exposure to PFAS by combining targeted human exposure assessment with chemometric approaches to characterize existing PFAS sources. To ensure a legacy of scientific awareness, the dissemination of broadly accessible research findings, and practical application by affected communities, STEEP Cores will match the intensity and rigor of the research projects. STEEP Cores will serve to a) prepare the next generation of interdisciplinary emerging contaminant researchers (Training Core), b) translate scientific findings generated by STEEP projects for dissemination to various internal and external stakeholders (Research Translation Core), and c) engage Cape Cod communities on the front lines of PFASs exposure through drinking water contaminated by Aqueous film forming foam use at Joint Base Cape Cod. The Administrative Core, led by its directors, and guided by Internal and External Advisory Committees, will ensure the integration of STEEP?s projects and cores.